LAN8820I datasheet(67/83 Pages) MICROCHIP

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 2009-2015 Microchip Technology Inc.

DS00001871B-page 67

LAN8820/LAN8820I

5.5.3

POWER-ON HARDWARE RESET TIMING

Figure 5-3 illustrates the nRESET, configuration strap/pin, and CONFIG[3:0] timing requirements in relation to power-

on. A hardware reset (nRESET assertion) is required following power-up. For proper operation, nRESET must be

asserted for no less than trstia. The nRESET pin can be asserted at any time, but must not be deasserted before tpurstd

after all external power supplies have reached operational levels. In order for valid configuration strap values to be read

at power-up, the tcss and tcsh timing constraints must be followed. In order for CONFIG[3:0] values to be read at power-

up, the tcs and tch timing constraints must be followed. Refer to Section 3.6.1, "Hardware Reset (nRESET)," on page 22

for additional information.

Note 1:

Device configuration straps are latched as a result of nRESET assertion. Refer to Section 3.8.1.1, "Config-

uration Straps," on page 24 details. Configuration straps must only be pulled high or low and must not be

driven as inputs.

nRESET deassertion must be monotonic.

FIGURE 5-3:

HARDWARE RESET TIMING

TABLE 5-12:

HARDWARE RESET TIMING VALUES

Symbol

Description

Min

Typ

Max

Units

tpurstd

External power supplies at operational level to nRESET

deassertion

tpurstv

External power supplies at operational level to nRESET

valid

0nS

trstid

nRESET input deassertion time

S

trstia

nRESET input assertion time

100

S

tcss

Configuration strap pins setup to nRESET deassertion

200

tcsh

Configuration strap pins hold after nRESET deassertion

totaa

Output tri-state after nRESET assertion

todad

Output drive after deassertion

800

tcs

CONFIG[3:0] setup to nRESET deassertion

tch

CONFIG[3:0] hold after nRESET deassertion

tcss

nRESET

Configuration

Straps

tcsh

Configuration Strap

Pins Output Drive

All External

Power Supplies

tpurstd

Vopp

tcs

CONFIG[3:0]

tch

trstia

todad

tpurstv

totaa

trstid

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